For the purpose of more adequately describing a technological level for the present invention at the present time, all descriptions of the patents, patent applications, patent gazettes, scientific papers, and the like which are quoted or identified in the present application will be incorporated by reference herein.
In a mobile communication network, a positioning function which provides position information of a mobile station is an important function enabling a variety of position information services. The 3 GPP (Third Generation Partnership Program) which defines a global standard of the mobile communication network sets the specifications of a position information service function and a positioning function. These are disclosed in 3GPP Technical Specification 23.271 v.5.4.0, “Functional stage 2 description of LCS,” in September, 2002 (hereinafter, referred to as Literature 1), and 3GPP Technical Specification 25.305 v.5.4.0, “Stage 2 functional specification of User Equipment (UE) positioning in UTRAN,” in March, 2002 (hereinafter, referred to as Literature 2). The Literature 1 stipulates a procedure by which a client device outside the network obtains position information of a mobile station from the mobile communication network. On the other hand, the Literature 2 stipulates a procedure for obtaining a geographical position of a mobile station inside the mobile communication network.
Concerning position information showing the geographical position of a mobile unit, the value of the position information is determined by two information of accuracy information and freshness information. The accuracy information is the information which shows the correctness of the position information, and the higher the accuracy, the higher the probability of existence of a mobile station at the point indicated by the position information is. There is considered an example in which the range of existence of a mobile station at a certain probability (e.g., 95%, and the like) is shown in circle, and a central point of the circle is defined as position information, with a diameter thereof defined as accuracy information. The freshness information is the information which shows the newness of the position information, and the higher the freshness, the higher the probability of existence of the mobile station at the point indicated by the position information is.
In the 3GPP position information service described in the Literature 1 and the Literature 2, an external client may specify positioning accuracy that it requests. However, as a result of positioning processing inside the network, the operation of a positioning system when position information satisfying the requested positioning accuracy is not obtained is not defined, and thus there is considered an instance in which an error is notified to the external client, or there is considered an instance in which position information with the accuracy which is closest to the requested positioning accuracy is notified. Both of the aforementioned possibilities are described in chapter 7.3.1 of the Literature 2, which is supposed to be implementation or an operator matter.
In an actual position information service, it is believed that how to behave when positioning accuracy that one requests is not satisfied depends on the position information provided by an external client. For example, it is believed that a position information service, such as human navigation which acts as a guide for pedestrians requires positioning accuracy of about 10 m to several tens of meters. However, as a result of positioning processing on the operator side, even if position information with positioning accuracy of several kilometers order is notified when request positioning accuracy is not satisfied, it is useless information for the service in the external client, it being presumably questionable that the external client and users have to sacrifice for such information.
While request freshness of the position information is not regulated in the current 3GPP standard, it is expected that, upon standardization of the request freshness, the processing when position information of the requested freshness is not obtained arouses a problem in the same way as the positioning accuracy.
In the aforementioned circumstances, it was desired to realize a positioning system which selects and responds appropriate positioning results as requested by the client in the positioning processing, and particularly to realize a positioning system carrying out the processing based on the positioning accuracy and the positioning freshness requested by the client.